Method and device for stabilizing a semi-trailer

ABSTRACT

In a method and apparatus for stabilizing a vehicle combination (composed of a towing vehicle with front and rear wheels and a trailer or semi-trailer at least one dynamic movement input variable is determined and evaluated. If a rolling movement of the vehicle combination is detected at least braking interventions for stabilizing the dynamic movement state of the vehicle combination are brought about for the towing vehicle. According to the invention, a yaw moment which counteracts the rolling movement of the vehicle combination is produced solely by means of braking interventions which are brought about for the front wheels of the towing vehicle.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German patent application 102 54810.2, filed Nov. 22, 2002 (PCT International Application No.PCT/EP2003/012987, filed Nov. 20, 2003, the disclosure of which isexpressly incorporated by reference herein.

The invention relates to a method and a device for stabilizing a vehiclecombination.

Vehicle combinations (a trailer and a towing vehicle) tend to carry outrolling movements as the speed increases. For the sake of simplicity,the term “rolling movement” will be used below to designate the unstablestate of a vehicle combination which can be eliminated using the methodor apparatus according to the invention. This is not, however, intendedto constitute a restriction, and the terms oscillating movement orrolling movement can also be used to designate this state.

More specifically, if a vehicle combination experiences a rollingmovement, the trailer oscillates about its vertical axis and alsoexcites oscillations in the towing vehicle via the trailer hitch. If thespeed of the vehicle is below what is referred to as a critical speed,the oscillations are damped. If the speed of the vehicle is equal to thecritical speed, the oscillations are undamped. If the speed of thevehicle is above the critical speed, the excited oscillations no longerdecay automatically, but reinforce one another. The vehicle combinationis subject to greater and greater rocking in its transverse movementwhich may lead, under certain circumstances, to an accident.

The rolling movement may be excited, for example, by steeringinterventions by the driver which are unsuitable for a specific drivingsituation, as a result of traveling over a bump or as a result of theeffect of side wind influences.

The magnitude of the critical speed depends, inter alia, on geometrydata such as wheelbase and tow bar length, on the mass and the yawinertia moment of the towing vehicle and of the trailer, and on theoblique running rigidities of the tires and/or axles. The critical speedvaries typically in the region from 70 to 130 kilometers per hour invehicle combinations in the passenger car field. The frequency of therolling movement is approximately 0.5 to 2 Hz.

If a rolling movement occurs, an essentially periodic transversemovement occurs at the towing vehicle which is towing the trailer. Suchtransverse movement may be expressed, for example, in the transverseacceleration or the yaw angle rate of the towing vehicle. As a result,during a rolling movement, an essentially periodic signal of thetransverse acceleration or of the yaw rate occurs. This is not astrictly periodic oscillation phenomenon, since the vehicle combinationdoes not constitute an ideal oscillating system. Instead, temporalfluctuations in the period length of the oscillating movement of thetrailer can occur. These are expressed, for example, in a repeating oressentially periodic signal which is produced by a transverseacceleration sensor. That is, this signal has a period length whichchanges within small limits, and which is however ideally to beconsidered as constant over time. The same also applies to the signal ofa yaw rate sensor.

Correspondingly, a yaw moment which is to be impressed and with whichthe yaw moment which originates from the rolling movement is to becompensated is also not strictly periodical. The period length in theyaw moment to be impressed is also changed in accordance with thefluctuations in the period of the rolling movement or oscillatingmovement of the vehicle combination.

A large number of differing methods and devices for stabilizing vehiclecombinations are known from the prior art. For example, the publication“Aktive Gespannstabilisierung beim BMW X5 [Active vehicle combinationstabilization on the BMW X5]” which appeared on pages 330 to 339 in theAutomobiltechnischen Zeitschift (ATZ) [Automobile Periodical] 104, 2002,Issue 4 describes a device for stabilizing vehicle combinations withwhich oscillations which occur independently of the properties of theparticular vehicle combination and the traveling speed are detected, andwhen certain limiting values are exceeded the vehicle combination can bereturned to the safe traveling state again by active braking of thetowing vehicle. The detection of the oscillation is based essentially onan analysis of the measured yaw rate. The yaw rate is filtered with abandpass filter which is dimensioned to the frequency band 0.5 Hz and1.0 Hz, and the amplitude of the filtered signal is determined.

By reference to this yaw amplitude it is decided whether a brakingintervention is necessary to stabilize the vehicle combination. Inaddition to the instantaneous value of the yaw amplitude, the behaviorof the yaw amplitude over time is also evaluated. If an unstable stateof the vehicle combination is detected, the towing vehicle is brakedsymmetrically at all four wheels by actively building up pressure untilthe oscillating movement has sufficiently decayed.

For this purpose, a constant value for the setpoint deceleration ispredefined, said value being set by a deceleration controller. At thesame time the drive torque is limited to zero. In addition to thesymmetrical braking intervention, the wheel-specific brakinginterventions which originate from a yaw rate controller can also becarried out during an oscillating movement and then superimposed on thesymmetrical braking intervention.

German patent document DE 195 36 620 A1 describes a method for improvingthe transverse stability of a vehicle combination. According to thismethod, vehicle-decelerating measures are taken if the amplitude of adynamic transverse vehicle variable, for example the transverseacceleration or the yaw angle rate, oscillates within a predefinedfrequency band and at the same time exceeds a limiting value. Thevehicle-decelerating measures are interventions for reducing the angleof aperture of the throttle valve in order to reduce the drive torqueand/or interventions for feeding brake pressure to the front wheels andthe rear wheels of the towing vehicle.

German patent document DE 100 31 266 A1 describes a method and apparatusfor detecting an oscillating movement of a vehicle. The vehicle isequipped with means for influencing the torque which is output by theengine, and with brakes which are assigned to the wheels of the vehicle.When an oscillating movement is detected, the means for influencing thetorque which is output by the engine and the brakes are actuated (bothto the same extent) in order to reduce the speed of the vehicle.Alternatively there is provision, when an oscillating movement of thevehicle is detected, to actuate the wheel brakes individually in such away that a yaw moment which acts on the vehicle and which counteractsthe oscillating movement is produced.

German patent document DE 100 34 222 A1 describes a method and a devicefor stabilizing a vehicle combination. If a rolling movement isdetected, stabilizing interventions are carried out. In a firstprocedure, correctly phased braking interventions are carried out at thebrakes of the towing vehicle. At the same time the brakes of the trailerare braked uniformly. As an alternative to the correctly phased brakinginterventions at the towing vehicle it is possible to performcorresponding steering interventions. In a second procedure only thetrailer is braked selectively.

German patent document DE 199 64 048 A1 describes a method and apparatusfor stabilizing a vehicle combination. If a rolling movement is detectedfor the vehicle combination, an essentially periodic yaw moment which isessentially antiphase to the rolling movement is impressed byautomatically braking the road vehicle with different braking forces onthe two sides of the road vehicle, such that the vehicle isautomatically braked on one side.

After and/or in addition to the impressing of the essentially periodicyaw moment the road vehicle is automatically briefly braked in such away that the overrun brake of the trailer is triggered. This briefbraking can be carried out by intervening in the wheel brakes of thetowing vehicle or by reducing the drive torque. Depending on the levelof equipment of the vehicle different braking interventions are carriedout. If the vehicle is equipped with a yaw rate controller (ESP, FDR),all the wheels of the towing vehicle can be braked individually in orderto impress the essentially periodic yaw moment. Furthermore, all thewheels can also be braked simultaneously or the engine power can bereduced by corresponding engine interventions so that the overrun brakeof the trailer is activated. If the vehicle has rear wheel drive or allwheel drive and is equipped with a traction controller system (TCS), theessentially periodic yaw moment can be impressed by brakinginterventions at the rear axle. If, in contrast, the vehicle has frontwheel drive and is equipped with a traction controller system (TCS), thestabilizing possibility described above is not available. In this case,all that is possible is to brake all the wheels of the towing vehicle.Even in the case of a vehicle which is equipped only with an anti-lockbrake system (ABS), all the wheels of the towing vehicle are braked inorder to stabilize the vehicle combination, which leads at the same timeto activation of the overrun brake of the trailer.

German patent document DE 100 07 526 A1 describes a method and apparatusfor stabilizing the dynamic movement state of vehicle combinations. Ifan unstable dynamic state is detected, the longitudinal speed of thetowing vehicle is reduced by intervening in the engine and/or in thebrakes of the towing vehicle. As an alternative to the interventions bywhich the longitudinal speed of the towing vehicle is reduced, it ispossible to carry out a one-sided braking intervention at the towingvehicle, which brings about a reduction in the bending angle.

A disadvantage of the methods or devices for stabilizing a vehiclecombination which are known from the prior art is that brakinginterventions are either carried out mainly or exclusively at the rearwheels or else the front wheels, and the rear wheels are always brakedtogether (i.e., simultaneously), specifically either uniformly orindividually. This type of braking intervention causes longitudinalforces, (i.e., circumferential forces), to be produced at the rearwheels, which at the same time brings about a reduction in lateralguiding forces that would be required to stabilize a rolling vehiclecombination. In other words, these braking interventions at the rearwheels reduce the lateral guiding force potential at said wheels. If theunderlying surface conditions correspond (for example when there is alow coefficient of friction of the underlying surface due to water orsnow-covered or icy underlying surface), this can lead to an increase oramplification of the unstable behavior of the vehicle combination (i.e.,the rolling movement of the vehicle combination), even though thebraking interventions performed for stabilization purposes are actuallyintended to eliminate the unstable behavior of the vehicle combination.

One object of the invention, therefore, is to provide an improved methodfor stabilizing vehicle combinations.

Another object of the invention is to provide a method in which, duringthe period of time in which the interventions for stabilizing thevehicle combination are carried out, a lateral guiding force potentialwhich is sufficient to stabilize the vehicle combination is present orensured predominantely at the rear wheels of the towing vehicle.

These and other objects and advantages are achieved by the methodaccording to the invention, in which at least one dynamic movement inputvariable is determined and evaluated. If a rolling movement of thevehicle combination is detected by means of the evaluation, at leastbraking interventions for stabilizing the dynamic movement state of thevehicle combination are brought about for the towing vehicle. Accordingto the invention, a yaw moment which counteracts the rolling movement ofthe vehicle combination is produced solely by means of brakinginterventions which are brought about for the front wheels of the towingvehicle, independently of the driver.

The fact that the yaw moment which counteracts the rolling movement ofthe vehicle combination is produced solely by means of the brakinginterventions for the front wheels ensures that a lateral guiding forcepotential which is sufficient to stabilize the vehicle combination isavailable, in particular at the rear wheels.

So that this lateral guiding force potential which is so significant isnot reduced, according to the principle employed, the execution ofbraking interventions at the rear wheels of the towing vehicle isdispensed with, or largely dispensed with. Braking interventions for therear wheels of the towing vehicle are permitted or brought about inaddition to the braking interventions mentioned above for the frontwheels only when a predefined operating state of the vehicle combinationis present. This ensures that in specific situations in which thebraking effect which is brought about at the front wheels is notsufficient to stabilize or decelerate the vehicle combination in anenduring fashion, it is possible to increase the total braking effectacting on the vehicle combination, and thus to bring about deceleration,which in turn leads to a situation in which the vehicle combination canbe stabilized better.

According to the present invention, braking interventions which giverise to braking forces that are composed of a basic force and a dynamicforce component are advantageously brought about for the front wheels.In comparison with braking interventions which produce only a uniform(i.e., constant) braking force, such braking interventions (which can bereferred to as “oscillating”) have the advantage that they make it ispossible to generate a counter-yaw moment which counteracts the rollingmovement of the vehicle combination. This counter-yaw moment isessentially in antiphase to the rolling movement of the vehiclecombination. A counter-yaw moment cannot be built up using brakinginterventions with which a uniform or constant braking effect isproduced. If, for example, all the wheels of the vehicle are brakedsimultaneously in such a way that a uniform or constant braking effectis produced at the wheels, the moments which are produced by thesebraking interventions and which act on the vehicle cancel one anotherout; a counter-yaw moment cannot be built up with this type of brakingintervention.

Since the aim is to use the permitted additional braking interventionsfor the rear wheels to increase the deceleration acting on the vehiclecombination, these braking interventions are carried out at the rearwheels in such a way that they bring about an essentially constantbraking effect. Modulation of the braking interventions for the rearwheels which is also performed would lead to a modulating reduction inthe lateral guiding force potential at the rear wheels, and is thereforenot carried out.

The build up of the additional braking effect at the rear axle isadvantageously carried out in such a way that the value of the vehicledeceleration which has occurred due to the braking process which isinitiated or carried out by the driver is maintained. The driver thuscontinues to be provided with the deceleration which he can sense. Thereare no distractions as a result of a possibly changing decelerationduring the stabilizing interventions which are carried out independentlyof the driver.

The braking process which is initiated or carried out by the driver iswhat is referred to as a driver-dependent braking operation which isbased on activation of the brake pedal by the driver. Such a brakingoperation can be sensed by the initial pressure set by the driver or bya signal which is output by a brake light switch or by a signal whichrepresents the deflection of the brake pedal.

A predefined operating state of the vehicle combination, in whichbraking interventions for the rear wheels are permitted, is present, forexample, if a rolling movement of the vehicle combination is detected,while at the same time there is no braking by the driver and the vehiclecombination is located on an underlying surface with a low coefficientof friction. That is, under these circumstances, braking interventionsfor the rear wheels are also permitted. In this configuration,stabilizing interventions which are independent of the driver are notnecessarily performed. Instead, precautions are taken to ensure thatsuch interventions can be made if there is a need for them. As a result,where necessary, quick stabilization of the vehicle combination ispossible.

A predefined operating state of the vehicle combination, in whichbraking interventions is applied to the rear wheels, is present, forexample, if a rolling movement of the vehicle combination is detected ata time when there is no braking by the driver and the brakinginterventions applied to the front wheels lead to a risk of the frontwheels locking. In this situation, in addition to the instability causedby the rolling movement of the vehicle combination, further instabilityoccurs, specifically that which is caused by possibly locking frontwheels.

This further instability is eliminated automatically by an anti-lockbrake system (ABS) with which the vehicle combination is equipped. Forthis purpose, the anti-lock brake system actuates the brake actuatorsassigned to the front wheels, in such a way that the braking force whichis exerted at the front wheels is reduced, or is applied to such anextent that locking of the front wheels is avoided. Since the brakingforce which is necessary at the front wheels in order to stabilize thevehicle combination cannot be built up alone in the present operatingstate of the vehicle combination (that is, a significant deceleration ofthe vehicle cannot be brought about by the braking interventions at thefront wheels), corresponding braking interventions are brought about atthe rear wheels of the towing vehicle. With this configuration it isbetter to brake all the wheels simultaneously in order to implement adeceleration of the vehicle combination, and thus a reduction in kineticenergy.

Whether there is a risk of the front wheels locking can be determined,for example, by evaluating the slip at the front wheels, or else byevaluating an ABS flag which indicates, in the present operating state,that braking interventions are performed at least for a front wheel byan anti-lock brake system, in order to avoid locking of this wheel. Thatis to say it is appropriate to check whether one of the front wheels issubjected to wheel slip control by the anti-lock brake system.

A further predefined operating state of the vehicle combination, inwhich braking interventions are applied to the rear wheels is, forexample, if a rolling movement is detected during a braking processwhich is initiated or carried out by the driver and the vehicledeceleration occurring as a result of that braking process fulfills apredefined comparative criterion. In this situation, additional brakinginterventions for the rear wheels are brought about.

If the vehicle deceleration is below a predefined threshold value, therear wheel braking effect which results from a driver initiated brakingprocess is thus at least partially reduced by the braking interventionsfor the rear wheels. This measure is taken therefore in order to ensurethat a lateral guiding force potential at the rear wheels of the towingvehicle is sufficient to stabilize the vehicle combination. This loss ofbraking effect which occurs at the rear wheels is compensated by thebraking effect which occurs at the front wheels as a result of the basicforce. At the same time it is ensured that the driver does notexperience any perceptible change in the deceleration set by him due tothe stabilizing interventions carried out independently of the driver.

The braking effect which occurs at the rear wheels as a result of thedriver initiated braking process is preferably reduced to such an extentthat the vehicle deceleration which has resulted from such brakingprocess is at least maintained. However, the intention is to make itpossible for a safety system which is contained in the towing vehicle(for example an ESP system) to be able to request a higher brakingeffect (and thus a greater vehicle deceleration), thus also being ableto set such an effect and such deceleration.

On the other hand, if the vehicle deceleration is above a predefinedthreshold value, the braking effect which occurs at the rear wheels as aresult of the driver initiated braking process is thus at leastmaintained by the braking interventions which are brought about for therear wheels. This measure is intended to ensure that strong driverbraking which may be necessary due to a particular traffic situation ismaintained. An example of this is strong braking of the vehiclecombination which is desired by the driver and which is intended toreduce the kinetic energy of the vehicle combination to a minimum in theevent of an unavoidable rear-end collision.

If an intervention of an anti-lock brake system (ABS) is madesimultaneously at one or both front wheels when there is vehicledeceleration above the predefined threshold value, an additional brakingeffect is increased at the rear axle by rear wheel brakinginterventions. The reduction in deceleration which originates from theinterventions of the anti-lock brake system due to the reduction in thebasic force at the front wheels is thus compensated.

For rear wheel braking interventions, the following procedure is alsopossible in the case under consideration: At first in accordance withthe invention, a reduction in the braking effect is first permitted atthe rear wheels by means of corresponding braking interventions.However, if an intervention of an anti-lock brake system is detected forat least one of the front wheels and at the same time it is ascertainedthat the present vehicle deceleration does not correspond to thatdesired by the driver, the braking effect at the rear wheels isincreased again by corresponding braking interventions.

If at least the towing vehicle is equipped with a hydraulic orelectrohydraulic or pneumatic or electropneumatic brake system, thefront wheel braking interventions lead to a situation in which a brakepressure composed of a basic pressure and dynamic pressure peaks is fedinto the wheel brake cylinders assigned to the front wheels. Thisdivision corresponds to the division represented above into a basicforce and dynamic force component. In this context the yaw moment whichcounteracts the rolling movement of the vehicle combination is producedby the dynamic force component or the dynamic pressure peaks. Althoughthe basic pressure which is fed in at the two front wheels creates amoment which acts on the vehicle with respect to the individual frontwheel, since the basic pressure is fed in symmetrically at both frontwheels, these two moments do not give rise to any yaw moment whensuperimposed on one another. The basic pressure which is fed in at thefront wheels thus does not bring about any rotation of the vehicle aboutits vertical axis.

The value of the basic force or pressure is advantageously determined asa function of a deviation in the yaw angle rate. This deviationadvantageously results from the difference between the actual value forthe yaw angle rate (which is determined using a yaw angle rate sensor)and a setpoint value for the yaw angle rate (which is determined using amathematical model). Determining the value of the basic force or thebasic pressure as a function of the deviation of the yaw angle rate hasthe following advantage: if, for example, the setpoint value issubtracted from the actual value, the setpoint value can then berepresented as a zero line with respect to the excitation energy, whilethe actual value represents the excitation energy of the rolling vehiclecombination. Consequently the deviation represents a measure of theexcitation energy which is to be reduced by stabilizing brakinginterventions. Since rolling movements of the vehicle combinationincrease at speeds above the critical speed, and stabilizing brakinginterventions are therefore necessary for compensation, the deviation isalso a measure of the kinetic energy to be reduced. The value of thedeviation thus permits the intensity of the braking interventions to becarried out to be defined.

The value for the dynamic force component or for the dynamic pressurepeaks is advantageously determined as a function of a variable whichdescribes the change over time of a deviation in the yaw angle rate.Various procedures are possible for determining this variable. Forexample, it can be determined as a derivative over time in the controlerror which is present for the yaw angle rate (i.e., the deviation inthe actual value of the yaw angle rate from the associated setpointvalue). This variable consequently corresponds, as it were, to adeviation between an actual and a setpoint value for the yaw angleacceleration. This variable can also be determined directly as adeviation of the yaw angle acceleration from an associated setpointvalue in a particular driving situation. The reason why the value isdetermined for the dynamic force component or dynamic pressure peaks asa function of this variable is as follows: the yaw moment whichoriginates from the rolling movement of the vehicle combination isproportional to the yaw acceleration. Thus, the most effectivecompensation of the rolling movement can be achieved by making thepressure peaks, which are intended to implement the compensation,proportional to the yaw acceleration. If the setpoint value of the yawangle rate is zero, the deviation for the yaw angle rate corresponds toits actual value. At the same time, the variable which describes thechange over time in the deviation for the yaw angle rate corresponds tothe actual value of the yaw angle rate.

It is has proven advantageous that both the basic pressure and thedynamic pressure peaks decrease as the rolling movement decreases. Thestabilizing interventions which are carried out independently of thedriver are thus adapted to the degree of instability.

Advantageously, engine interventions are also carried out in addition tothe braking interventions, thereby enhancing the deceleration effect forthe vehicle combination. The torque which is output by the engine isadvantageously set by these engine interventions in such a way that no(or nearly zero) circumferential forces occur at the driven wheels ofthe towing vehicle. In other words, the frictional losses which occur inthe drive train are compensated and the driven wheels are given aneutral setting as far as the circumferential force is concerned. (Thatis, they are essentially given a setting which is free ofcircumferential force). The last-mentioned measure ensures that a highdegree of lateral guidance potential force is available. The suitabledrive torque which is applied to the driven wheels via the drive trainimproves the compensation of the rolling movement of the vehiclecombination. Depending on the design of the vehicle engine, the engineinterventions influence, for example, the position of the throttle valveor the ignition angle or the injection quantity.

After the stabilizing braking interventions have been initiated, it isadvantageously checked whether the instability of the vehiclecombination decreases. If it is detected in the process that the vehiclecombination has reached a stable state again, no further stabilizingbraking interventions are produced. At the same time, the drive torqueis set in accordance with the value which is predefined by the driver,derived from the activation of the accelerator pedal. This measuresensures there is a transition, with accent on comfort, from the travelsituation which was present before the stabilizing interventions whichwere independent of the driver were carried out, and the travelsituation which is present after the aforesaid interventions have beencarried out. Disruptive, possibly sudden, changes in the longitudinaldynamics are avoided.

At least the yaw angle rate of the towing vehicle is advantageouslydetermined and evaluated as a dynamic movement input variable. Thevehicle speed, the yaw angle rate and the steering angle areadvantageously evaluated in order to determine whether a rollingmovement is occurring. In this context, a rolling movement is occurringif the yaw angle rate exhibits an oscillating behavior when the vehiclespeed is higher than an associated threshold value and the driver is notmaking any steering interventions. The threshold value which is givenabove for the vehicle speed is advantageously lower than the criticalspeed. It lies, for example, in a range above 55 kilometers per hour,preferably between 55 and 60 kilometers per hour.

Advantageously, the presence of a rolling movement of the vehiclecombination is detected as a function of a deviation variable whichrepresents the deviation between the actual value of the yaw angle rateand an associated setpoint value. If this deviation reaches or exceeds apredefined threshold value, this is an indication that a rollingmovement of the vehicle combination is occurring. By taking into accountor evaluating the control error it is possible, for example, to detect aslalom movement which is desired by the driver (and during which thevehicle combination is not unstable, and there is thus also no need forstabilizing interventions).

The method and apparatus according to the invention also make itpossible for an average driver to cope with an unstable vehiclecombination (i.e., a vehicle combination which has a rolling movement),and permit rapid attenuation of a yaw reaction. A further advantage isthat, because of the vehicle dynamic systems which are already in seriesproduction today (for example, a yaw rate controller known as ECP, whichis found on vehicles of the applicant) there is no need for anyadditional actuation or sensor systems. Moreover, no changes to thetrailer are necessary. (That is, there is no need to mount an actuatoror sensor system on the trailer, so that trailers which are already inoperation do not need to be retrofitted.)

If it is detected that there is a rolling movement for the vehiclecombination or if the vehicle detects the inclination or tendency toexecute a rolling movement, stabilizing interventions are performed.These are in the first instance braking interventions which are carriedout independently of the driver and in the second instance engineinterventions.

The braking interventions are intended to reduce the yaw moments whichoriginate from the rolling movement and act on the vehicle. They aretherefore performed in such a way that as to produce a counter-yawmoment which acts on the vehicle. For this purpose, braking interventionare first carried out on the front wheels of the vehicle as a functionof the value of the sensed yaw moment acting on the vehicle and/or ofthe value of the sensed yaw acceleration in such a way that theycounteract the yaw moment originating from the rolling movement. As aresult, the energy of the rolling movement (i.e., the oscillationenergy) is reduced, and the vehicle combination stabilizes and travelsin a stable way again.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows two situations of an unstable vehicle combination, forexplaining the basic procedure of the method according to the invention;

FIG. 2 is a diagram which shows signal profiles of different variableswhich are significant in conjunction with the method according to theinvention;

FIG. 3 is a functional block diagram that shows the method of operationon which the method according to the invention is based;

FIG. 4 shows the detection logic which is used in the method accordingto the invention, in the form of a functional block illustration;

FIGS. 5 a, 5 b, 5 c and 5 d illustrate the determination of differentvariables in the detection logic in the form of functional blockillustrations;

FIG. 6 is a functional block diagram that shows the structure ofintervention logic which is used in the method according to theinvention;

FIGS. 7 a and 7 b are functional block illustrations that show thecomponents of the intervention logic for determining actuation signalsfor carrying out braking interventions and engine interventions;

FIGS. 8 a, 8 b and 8 c show the procedure for determining the actuationsignals for carrying out the braking interventions, in the form offunctional block illustrations;

FIG. 9 shows, on the one hand, a schematic illustration of the deviceaccording to the invention and, on the other hand, the essential stepsof the method according to the invention which runs in the deviceaccording to the invention, in the form of a block circuit diagram.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the basic procedure for the braking interventionswhich are carried out at the front wheels according to the inventivemethod. In the left-hand representation, the trailer 102 oscillates tothe right, which causes the towing vehicle 101 to execute a left-handedrotation about its vertical axis, as indicated by the arrow. Due to thedetected rolling movement of the vehicle combination 104, a basicbraking force is fed in at both front wheels 103 vl, 103 vr of thetowing vehicle. In addition, a dynamic braking force which leads to ayaw moment which is directed to the right and acts on the towing vehicle101 is fed in at the right-hand front wheel 103 vr. This yaw momentwhich is brought about by the dynamic braking force counteracts the yawmoment which is brought about by the rolling movement, and thusstabilizes the vehicle combination 104.

In the right-hand illustration, the trailer 102 oscillates to the left,which causes the towing vehicle 101 to execute a right-handed rotationabout its vertical axis, as indicated by the arrow. Due to the detectedrolling movement of the vehicle combination 104, a basic braking forceis fed in at both front wheels 103 vl, 103 vr of the towing vehicle. Inaddition, a dynamic braking force which leads to a yaw moment which isdirected to the left and acts on the towing vehicle 101 is fed in at theleft-hand front wheel 103 vl. This yaw moment which is brought about bythe dynamic braking force counteracts the yaw moment which is broughtabout by the rolling movement, and thus stabilizes the vehiclecombination 104.

This procedure is also illustrated in the diagram in FIG. 2, whichshows, at the upper part of the diagram, the signal profiles for the yawrate and the steering angle. The lower part of this diagram shows thesignal profiles for the brake pressures which are set at the individualwheels 103 vl, 103 vr, 103 hl, 103 hr of the towing vehicle and thesignal profile of the basic brake pressure, which are fed in together atthe front wheels 103 vl, 103 vr. As is apparent from the signalprofiles, the brake pressures supplied to the two front wheels 103 vl,103 vr is composed of a basic brake pressure and of dynamic pressurepeaks.

The upper part of the diagram illustrates the following travelsituation: the driver produces a rolling movement of the vehiclecombination 104 by corresponding steering wheel (and thus steering)movements 2 (in this instance a double steering jump). The rollingmovement of the vehicle combination 104 is thus due to the steeringmovements initiated by the driver. The rolling movement of the vehiclecombination 104 is shown in an oscillating behavior of the signalprofile of the yaw angle rates which is sensed using a yaw angle ratesensor. The following convention applies here: a positive value of theyaw angle rate indicates a deflection of the trailer 102 to the rightand thus at the same time a deflection of the towing vehicle 101 to theleft, while a negative value of the yaw angle rate signifies adeflection of the trailer 102 to the left and thus at the same time adeflection of the towing vehicle 101 to the right.

The method of excitation of a rolling movement which is described aboveis not intended to have a restrictive effect on the method according tothe invention. Of course, and this was the actual motivation forimplementing the method according to the invention: to make it possibleto eliminate rolling movements of a vehicle combination 104 which areexcited from the outside (i.e., independently of the driver).

The lower part of the diagram shows the braking interventions which arecarried out using the method according to the invention, based on thedetected rolling movement of the vehicle combination 104. At first it isapparent that a certain period of time passes between the occurrence ofthe oscillating yaw angle rate and the application of pressure. This isdue to the fact that at first the rolling movement has to be detectedusing a corresponding evaluation on which further details will be givenbelow. In addition, by reference to the profiles 5 and 6 it is apparentthat no brake pressure is being fed in at the two rear wheels 103 hl,103 hr. As already stated above, on the one hand a basic pressure isapplied which leads to the basic braking force mentioned above and, onthe other hand, wheel-specific pressure peaks are applied, which lead tothe dynamic braking forces mentioned above are supplied to the two frontwheels 103 vl, 103 vr.

The basic pressure is illustrated by the profile 7, and the pressurepeaks are shown in profiles 3 and 4. As is apparent from the diagramillustrated in FIG. 2, when the trailer 102 is deflected to the rightand there is thus a deflection of the towing vehicle 101 to the left, apressure peak is fed in at the right-hand front wheel 103 vr.Correspondingly, when the trailer 102 is deflected to the left and thereis thus a deflection of the towing vehicle 101 to the right a pressurepeak is fed in at the left-hand front wheel 103 vl.

The value of the basic pressure to be supplied is determined as afunction of a deviation in the yaw angle rate. This deviation resultsfrom the difference between the actual value for the yaw angle rate(which is determined using a yaw angle rate sensor) and a setpoint valuefor the yaw angle rate (determined using a mathematical model, in thepresent case a vehicle model).

The values for the pressure peaks which are to be applied are determinedas a function of a value or a variable which describes the change overtime of the deviation in the yaw angle rate. This variable can bedetermined, for example, as a time derivative in the control error whichis present for the yaw angle rate (i.e., the deviation in the actualvalue of the yaw angle rate from the associated setpoint value). Thisvariable can also be determined directly as a deviation of the yaw angleacceleration which is present in the respective travel situation from anassociated setpoint value, with the actual value being subtracted fromthe setpoint value. Due to its lower complexity, the first alternativeis to be preferred.

The basic braking force due to the basic brake pressure which is appliedat the front wheels 103 vl, 103 vr causes braking of the vehiclecombination 104. As a result, the speed of the vehicle combination 104is reduced to a value which is lower than the critical speed mentionedat the beginning.

The braking forces which are generated by the pressure peaks at thefront wheels 103 vl, 103 vr lead, on the one hand, to braking of thevehicle combination 104. On the other hand, the oscillating feeding ofthe pressure peaks causes what is referred to as a counter-yaw moment tobe impressed. Such counter-yaw moment is in antiphase (or opposed) tothe yaw moment originating from the rolling movement. This counter-yawmoment reduces the rolling movement of the vehicle combination 104extremely quickly. The vehicle combination 104 is stabilized.

After the stabilizing braking interventions have been initiated, it ischecked whether the instability of the vehicle combination 104 (i.e.,the rolling movement of the vehicle combination 104) decreases. If it isdetected that a stable state of the vehicle combination 104 has beenreached again, no further braking interventions are produced in order toproduce the basic brake pressure and the pressure peaks. At the sametime, the drive torque is set again in accordance with a valuepredefined by the driver, which can be derived from the activation ofthe accelerator pedal by the driver.

The procedure which is described above for the braking interventions isalso shown in the diagram in FIG. 2. Starting from the time t1, thesignal profile of the yaw angle rate has only a very small amplitude, sothat no further braking interventions are performed at this time. As canalso be inferred from this diagram, both the basic brake pressure andthe pressure peaks decrease generally as the rolling movement decreases.The speed of the vehicle combination is below the critical speed.

In the procedure illustrated in the diagram in FIG. 2 and in theunderlying travel situation, braking interventions are carried out onlyat the front wheels 103 vl, 103 vr. That is, a yaw moment whichcounteracts the rolling movement of the vehicle combination 104 isproduced solely by means of the braking interventions which are broughtabout for the front wheels 103 vl, 103 vr of the towing vehicle 101, andthe vehicle combination 104 is thus stabilized. The travel situationunder consideration is thus not intended to correspond to an operatingstate of the vehicle combination 104 in which additional brakinginterventions for the rear wheels 103 hl, 103 hr are permitted orbrought about. More details relating to braking interventions at therear wheels 103 hl, 103 hr and on the corresponding operating states ofthe vehicle combination 104 are given below.

As already mentioned, engine interventions can also be carried out inaddition to the braking interventions. For this purpose, for example, inthe case of a spark ignition engine, the throttle valve is set in such away that a zero torque is produced at the driven wheels. If the towingvehicle is a vehicle with rear wheel drive, the two rear wheels 103 hl,103 hr are the driven wheels. The throttle valve angle which is set inthis context is between 6° and 10°. In other words: as a result of theengine interventions the throttle valve is set in such a way that littleor no circumferential forces occur at the driven wheels. That is, thethrottle valve is set in such a way that the friction losses which occurin the drive train are compensated and the driven wheels are given aneutral setting as far as the circumferential force is concerned.

With respect to FIG. 2 it is to be noted that a yaw moment whichcounteracts the rolling movement of the vehicle combination 104 isproduced solely by means of the braking interventions for the frontwheels 103 vl, 103 vr of the towing vehicle 101, as a result of whichthe vehicle combination 104 is stabilized. In addition, brakinginterventions can also be permitted or brought about at the rear wheels103 hl, 103 hr. Details are given below on the patterns according towhich the stabilizing braking interventions are carried out,independently of the driver, both for the front wheels 103 vl, 103 vrand for the rear wheels 103 hl, 103 hr.

If there is no braking by the driver, the front wheels 103 vl, 103 vrare braked. For this purpose, the basic pressure whose value isdetermined as a function of the deviation of the actual value of the yawangle rate from the setpoint value of the yaw angle rate is fed in forboth front wheels 103 vl, 103 vr. In addition, the pressure peaks whosevalues are each determined as a function of the deviation of the yawacceleration are each applied to the front wheels 103 vl, 103 vr. Insuch an operating state (there is no braking by the driver), attemptsare made to stabilize the vehicle combination 104 by means of brakinginterventions which are carried out exclusively at the front wheels 103vl, 103 vr. However, if there is such a low coefficient of friction ofthe underlying surface (for example, due to snow or the like) thatbraking force necessary to stabilize the vehicle combination 104 cannotbe built up at the front wheels 103 vl, 103 vr alone, then the rearwheels 103 hl, 103 hr are also braked. In such a context brake pressurecan be redistributed away from the front wheels 103 vl, 103 vr to therearwheels 103 hl, 103 hr. The fact that braking is occurring on anunderlying surface with a low coefficient of friction can be detected,for example, by evaluating the ABS flag. With the ABS flag an anti-lockbrake system indicates that braking interventions are performed at leastfor one vehicle wheel in order to prevent this wheel from locking. Inprinciple, in order to detect whether the vehicle is located on anunderlying surface with a low coefficient of friction it is alsopossible to evaluate a variable which describes the coefficient offriction. Such a variable is present, for example, in a dynamic movementsystem where the yaw rate of a vehicle is controlled.

If a rolling movement of the vehicle combination 104 occurs during abraking process which is initiated by the driver, the vehiclecombination 104 is stabilized by means of braking interventions asfollows: at first the vehicle deceleration which results from thebraking process initiated by the driver is determined. If this vehicledeceleration is below a predefined threshold value (which means that abraking process with a low deceleration has been initiated by thedriver), the brake pressure set at the rear wheels 103 hl, 103 hr as aresult of the braking process which is occurring is at least partiallyreduced. At the same time, brake pressure is built up at the frontwheels 103 vl, 103 vr in such a way that, on the one hand, the basicpressure is fed into both front wheels 103 vl, 103 vr and a pressurepeak is specifically fed into the respective front wheel. In this caseit is also possible, if braking is being carried out on an underlyingsurface with a low coefficient of friction, to implement aredistribution of brake pressure away from the front wheels 103 vl, 103vr to the rear wheels 103 hl, 103 hr.

If, on the other hand, the vehicle deceleration is above the predefinedthreshold value (which means that a braking process with a highdeceleration has been initiated by the driver), the brake pressure setat the rear wheels 103 hl, 103 hr is left. At the front wheels 103 vl,103 vr the brake pressure is modulated in order to produce a dynamic yawmoment which is in antiphase to the yaw moment due to the rollingmovement of the vehicle combination 104. If an intervention of ananti-lock brake system (ABS controller) is made at one front wheel orboth front wheels 103 vl, 103 vr during such a braking operation, brakepressure is additionally applied to the rear axle. As a result, it ispossible for the anti-lock brake system to reduce the brake pressure atthe front wheels 103 vl, 103 vr in a modulating fashion to such anextent that locking of one or both front wheels 103 vl, 103 vr isavoided, without reducing the deceleration which acts on the vehiclecombination 104. Pressure can even be applied to the rear axle to suchan extent that the rear wheels 103 hl, 103 hr are brought to theirlocking limit.

As an alternative to evaluating the vehicle deceleration it is alsopossible to detect whether a braking process is occurring with a high orlow deceleration, by evaluating the state of the front wheels 103 vl 103vr. For this purpose it is possible, for example, to evaluate the valueof the brake pressure which is supplied to the respective wheel brakecylinders of the front wheels 103 vl, 103 vr, or to evaluate theactuation of the inlet and outlet valves of the front wheels 103 vl, 103vr. Alternatively, it is also possible to evaluate the brake slipoccurring at the front wheels 103 vl, 103 vr.

To summarize, it is to be noted with respect to the brakinginterventions that, in the first instance stabilizing brakinginterventions are carried out at the front wheels 103 vl, 103 vr. Byevaluating a predefined criterion or when predefined operating states ofthe vehicle combination 104 are present it is possible that, in additionto the braking interventions carried out for the front wheels 103 vl,103 vr, braking interventions are also carried out at the rear wheels103 hl, 103 hr in order to produce a braking force.

A rolling movement of the vehicle combination 104 is sensed by thesensor system which is provided in the towing vehicle 101 in connectionwith the dynamic movement system with which the towing vehicle 101 isequipped (commonly referred to as a yaw rate controller, ESP).Consequently, at least vehicle speed, yaw angle rate and the steeringangle are evaluated in order to determine whether a rolling movement isoccurring.

The method according to the invention is composed of two main parts, asillustrated in FIG. 3: first, a detection logic component 301 whichdetects a rolling movement of the vehicle combination 104, and second,an intervention logic component 302 which carries out stabilizingbraking interventions, engine interventions, and/or steeringinterventions if a rolling movement of the vehicle combination 104 isoccurring. The variables which are required in the detection logiccomponent 301 for processing are made available to it via a CAN buswhich is provided in the towing vehicle 101, while the variablesrequired in the intervention logic component 302 are provided both onthe basis of the detection logic component 301 and also likewise via theCAN bus. Both the variables produced by the detection logic component301 and those produced by the intervention logic component 302 areoutput onto the CAN bus, in each case via a suitable interface which iscontained in the respective logic component.

The method of functioning of the detection logic component 301 will bedescribed below with reference to FIG. 4. The detection logic component301 detects whether a rolling movement of the vehicle combination 104(i.e., a rolling movement of the trailer 102) is occurring. Differentvehicle variables are evaluated for this purpose. In particular, the yawangle rate, the steering angle and the vehicle are evaluated.

The criterion for detecting the occurrence of a rolling movement of thevehicle combination 104 (and thus, a rolling movement of the trailer102) can be generally formulated as follows: an operating state of thevehicle combination 104 in which the vehicle speed is higher than orequal to an associated threshold value is considered. The thresholdvalue is lower here than the critical speed. If the yaw angle rateexhibits an oscillating behavior in this operating state even though thedriver does not activate the steering wheel and thus does not carry outany steering interventions, this is an indication that a rollingmovement of the vehicle combination 104 (and thus, the trailer 102) andan unstable state of the vehicle combination 104 are occurring. Thismeans that in order to detect whether a rolling movement of a vehiclecombination 104 is occurring, it is appropriate to evaluate the vehiclespeed, the yaw angle rate and the steering angle.

Since rolling movements can occur in a vehicle combination 104 whosespeed is below the critical speed but such movements are dissipatedagain automatically, it can be assumed from the outset that in anoperating state in which the vehicle does not reach the critical speed,stabilizing interventions, such as are carried out according to theinventive method, are unnecessary. If, on the other hand, the speed ofthe vehicle combination is above the critical speed, the rollingmovements of the vehicle combination increase, so that appropriatestabilizing interventions are carried out.

As is apparent from FIG. 4, different variables are fed to the detectionlogic component 301. In the first instance these are the variables whichare to be evaluated, comprising a variable Delta_Gier_PID, a variableLW_Diff and a variable v. The variable Delta_Gier_PID is determined as afunction of the yaw angle rate, in a block 401 which is described inconjunction with FIG. 5 a. The variable LW_Diff is determined as afunction of the steering angle, in a block 402 which is described inconjunction with FIG. 5 d. The variable v is the speed of the vehiclecombination 104 which is also referred to as the reference speed. In thesecond instance these variables are Erk_Delta_Gier_PID,Erk_Delta_Gier_PIDa, Erk_LW_Diff, Erk_LW_Diffa and Erk_V. Thesevariables represent parameters which can be set, which have the functionof threshold values and with which the abovementioned variablesDelta_Gier_PID, LW_Diff and v are compared.

As is apparent from the two-part illustration in FIG. 4, twointerrogations are made in the detection logic component 301. A firstinterrogation A1 detects whether a rolling movement of the vehiclecombination 104 is occurring. According to this first interrogation arolling movement of the vehicle combination 104 is occurring if i) thevariable Delta_Gier_PID is greater than or equal to the threshold valueErk_Delta_Gier_PID; ii) at the same time the variable LW_Diff is lowerthan the threshold value Erk_LW_Diff; and iii) at the same time thevehicle speed V is higher than or equal to the threshold value Erk_V. Ifit is detected that a rolling movement is occurring, stabilizinginterventions are necessary, so that the flag Stab_Erk_P is set, i.e.this flag is assigned the value 1.

In addition, a second interrogation by A2 detects whether the rollingmovement has decayed again. According to this second interrogation arolling movement of the vehicle combination 104 is no longer occurringif the variable Delta_Gier_PID is lower than the threshold valueErk_Delta_Gier_PIDa, or if the variable LW_Diff is higher than or equalto the threshold value Erk_LW_Diffa. If it is detected that a rollingmovement is no longer occurring, stabilizing interventions are no longernecessary, and the flag Stab_Erk_P is therefore deleted (assigned thevalue 0).

As is apparent from the two interrogations A1 and A2, differentthreshold values are used for the two variables Delta_Gier_PID andLW_Diff, so that a hysteresis function results.

The flag Stab_Erk_P is output by the detection logic component 301 andis thus available to the components in which this flag is furtherprocessed. In particular it is available to the intervention logiccomponent 302.

The method of determining different variables which are required in thedetection logic component 301 will be described using FIGS. 5 a, 5 b, 5c and 5 d. FIGS. 5 a, 5 b and 5 c illustrate how the variableDelta_Gier_PID is determined.

According to FIG. 5 a, in the first instance the actual value GIER_ROHof the yaw angle rate, which is measured using a yaw angle rate sensor,and in the second instance a setpoint value Gier_Stat of the yaw anglerate, which is determined from predefined driver values, are input intothe means for determining the variable Delta_Gier_PID. The actual valueGIER_ROH is made available via the CAN bus and the setpoint valueGier_Stat is determined in a block 501. The difference Delta_Gier whichis fed to a downstream bandpass filter 503 is formed from these twovariables by a difference former 502.

As is apparent from the illustration in the block 501 in FIG. 5 b, thesetpoint value Gier_Stat is determined using a mathematical model as afunction of the steering angle LW and the vehicle speed VREF, which areset by the driver. For example the Ackermann relationship, which isknown from the literature, can be used as a mathematical model.

As is apparent from FIG. 5 a, the difference Delta_Gier is fed to abandpass filter 503 which transmits only signals which lie in afrequency range from 0.5 to 2 Hz. This frequency range corresponds tothe frequency range which is typical of the rolling movement of avehicle combination 104; it is also referred to as the natural frequencyrange of the vehicle combination 104. The difference Delta_Gier, whichin terms of its significance is the control error of the dynamicmovement system which is arranged in the towing vehicle 101 and has thepurpose of controlling the yaw rate (ESP), is thus filtered, using abandpass filter, for the subsequent detection of a possible rollingmovement of the vehicle combination 104. If the vehicle combination 104rolls, a signal which changes over time and is in the form of anoscillation is thus present after the bandpass filtering, said signalgenerally being a pure sinusoidal or cosinusoidal oscillation. Thesignal Delta_Gier_BP which is determined using the bandpass filter 503is fed to a downstream block 504 whose function will be described usingFIG. 5 c.

The variable Delta_Gier_BP, (i.e., the filtered control error) which isprepared by the bandpass filter 503 is further processed, using the unitillustrated in FIG. 5 c, to form a variable Delta_Gier_PID which is usedto detect a rolling movement of the vehicle combination 104. At the sametime, this variable is used to determine the basic pressure to be fedinto the front wheels. Evaluating the control error, i.e., the deviationof the actual value of the yaw angle rate from the associated setpointvalue, has the following advantage over simply evaluating the signaldetermined using the yaw rate sensor, i.e. the actual value of the yawrate: by evaluating the control error it is possible, for example, todetect a slalom movement which is desired by the driver and during whichthere is no instability of the vehicle combination, and there is thusalso no need for stabilizing interventions.

At first, the absolute value of the signal Delta_Gier_BP is determinedusing a lowpass filter 505. By multiplying by a factor Erk_P aproportional component is obtained, which can be used to check howstrong the rolling movement is. The proportional component indicates ifan oscillation of significant size occurs after a disruption has actedon the vehicle combination. In addition, the absolute value signal whichis produced using the lowpass filter 505 is fed to a block 506 whichforms the time derivative of the absolute value signal. The signal whichis produced with the block 506 is multiplied by a factor Erk_D, as aresult of which a differential component is obtained with which it ispossible to check whether the rolling movement is decreasing orincreasing. The differential component also indicates instabilitieswhich are due to short-term disruption, for example, gusts of wind,which act on the vehicle combination. Alternatively it is also possibleto feed the absolute value signal from the lowpass filter 505 to a block507 where it is integrated. By multiplying the signal determined in theblock 507 by a factor Erk_I an integral component is obtained which hasthe following significance: for example when the vehicle combination istraveling at a speed which is near to the critical speed it is possiblefor continuous, slight rolling of the vehicle combination to occur. Sucha rolling behavior is sensed using the integral component. If theintegral component exceeds a predefined value, this is an indicationthat this slight rolling process has already been occurring for arelatively long time, for which reason stabilizing interventions inorder to eliminate it are necessary, and are carried out. Taking intoaccount the integral component is optional and is not necessarilyprovided with the method according to the invention.

The proportional component, the differential component, and, if one ispresent, also the integral component, are subsequently combined to formthe signal Delta_Gier_PID, which is output from block 504, is fed forfurther processing to the detection logic component 301, and to acomponent 805 which is shown in FIG. 8 b.

FIG. 5 d illustrates the method of determining the variable LW_Diff.

In determining whether a rolling movement of the vehicle combination 104is occurring, the variable LW_Diff is also evaluated in the detectionlogic component 301, because an evaluation of the yaw angle rate aloneor of a variable which is determined as a function of the yaw angle rateis too imprecise. If the steering angle were not also evaluated, itwould not be possible to differentiate between an instability which isdue to a rolling movement of the vehicle combination 104 and a slalommovement which is initiated intentionally by the driver by means ofsteering interventions. According to the illustration in FIG. 5 d, thesteering angle is evaluated in such a way (and thus the variable LW_Diffis determined in such a way), that at first the derivative of thesteering angle over time is formed in a block 508 and said derivative issubsequently lowpass filtered in a block 509. These measures filter outsmall steering movements of the driver which are insignificant.

The illustration in FIG. 6 shows the structure of the intervention logiccomponent 302. As is apparent, two types of intervention are carried outin order to stabilize the vehicle combination 104. On the one hand andin the first instance, braking interventions which are brought aboutusing a block 602, and on the other hand and in a supporting fashion, ifnecessary, engine interventions are brought about using a block 601.

FIG. 7 a shows the implementation of the block 601 and thus theprocedure when the actuation signals for carrying out the engineintervention are determined. The illustrated circuit has the followingfunction: if the flag Stab_Erk_P assumes the value 1 (meaning that arolling movement of the vehicle combination 104 is occurring), thesignal EIN_M_ESP_MOT whose value corresponds up to this point to theengine torque predefined by the driver assumes the valueEIN_M_ESP_MOT_WERT. As a result the engine torque is reduced in such away that no circumferential forces, or circumferential forces which arenear to zero, occur at the driven wheels of the towing vehicle 101. Thevalue EIN_M_ESP_MOT_WERT is determined, for example, as a function ofthe degree of efficiency of the drive train and/or of the selectedgearspeed and/or of the drag torque of the towing vehicle. If the flagStab_Erk_P assumes the value 0 (there is no longer any rolling movementin the case under consideration), the signal EIN_M_ESP_MOT assumes thevalue AUS_M_ESP_MOT_WERT. As a result, the drive torque is set again inaccordance with the value predefined by the driver. In this context thetransition is carried out using a suitably selected transition functionso that the transition does not cause the driver to be adverselyaffected.

FIG. 7 b illustrates the implementation of the block 602, and thus theprocedure for determining the actuation signals for carrying out thebraking interventions. Two blocks 701 and 702 determine the actuationsignals for stabilizing braking interventions at the front wheels 103vl, 103 vr, the actuation signals for the right-hand front wheel 103 vrbeing determined in block 701, and the actuation signals for theleft-hand front wheel 103 vl being determined in block 702. Theactuation signals for carrying out braking interventions at the rearwheels 103 hl, 103 hr are determined in blocks 703 and 704.

The blocks 701, 702, 703 and 704 in FIG. 7 b can be used to supply brakepressure to the wheels of the vehicle on a wheel-specific basis. Thebasic pressure or the basic force and the pressure peaks or the dynamicforces can thus be set at the front wheels 103 vl, 103 vr. In addition,the brake pressures can be distributed between the front wheels and therear wheels, as is necessary in certain predefined operating states ofthe vehicle combination.

The yaw acceleration Gier_Beschl is determined in block 705. For thispurpose, the signal GIER_ROH which is fed to this block is firstlylowpass filtered. The derivative of the lowpass filtered signal overtime is then formed and is itself lowpass filtered. The signalGier_Beschl which is produced in the process is then output by the block705 and fed, for example, to the blocks 701 and 702. In addition, theflag Stab_Erk_P which is contained in the signal grouping Stab_Erkn, andthe variable Delta_Gier_PID are also fed to the two blocks 701 and 702.

The structure of the two blocks 701 and 702 is explained below usingFIGS. 8 a, 8 b and 8 c, and details on these will be given first below.Details on the implementation of the two blocks 703 and 704 will then begiven.

FIG. 8 a illustrates the structure of the block 702 with which theactuation signals EIN_P_SOLL_VL are determined for carrying out thebraking interventions for the left-hand front wheel 103 vl. Thestructure of the block 701 which is assigned to the right-hand frontwheel 103 vr is identical. The same applies to the illustrations inFIGS. 8 b and 8 c.

The illustration in FIG. 8 a shows that the actuation signals arecomposed of two components—a first component for setting the basicpressure or the basic force which is determined in a block 801, and asecond component for setting the pressure peaks or the dynamic forces,which is determined in a block 802. These two components are added in asumming element 804. A block 803 is used to limit this summing signal.This measure ensures that the brake pressure which is to be set at thefront wheels 103 vl, 103 vr does not exceed a value which is predefinedfor the respective brake system. The limited summing signal is output asan actuation signal EIN_P_SOLL_VL.

FIG. 8 b illustrates the structure of the block 801 and thus theprocedure for determining the component of the actuation signal withwhich the basic pressure is set. As is apparent from the illustration inFIG. 8 b, this component is proportional to the variable Delta_Gier_PID.That is, this component is determined as a function of a deviation whichis present for the yaw angle rate. The proportionality to the variableDelta_Gier_PID causes the basic force to increase in the case ofrelatively severe oscillation, in this case the P component is larger.The same also applies to undamped oscillation.

If the flag Stab_Erk_P has the value 1 (a rolling movement of thevehicle combination 104 is occurring), the signal produced in themultiplier 805 as a product of the variables Delta_Gier_PID andEin_Basis_Druck_VL is output. The variable Ein_Basis_Druck_VL is anapplied gain factor which is dependent on the configuration of the brakesystem and preferably has a constant value within the range from 70 to140 bar. If, on the other hand, the flag Stab_Erk_P has the value 0, thesignal Aus_Basis_Druck, which has a predefined small value, is output,causing brake pressure to be fed in. This is intended to ensure that noinadvertent feeding in of brake pressure occurs if there is no rollingmovement. The signal which is to be output is smoothed using a block806.

FIG. 8 c illustrates the structure of the block 802 and thus theprocedure for determining the component of the actuation signal withwhich the pressure peaks are set. As shown in FIG. 8 c, this componentis proportional to the variable Gier_Beschl_TP and thus to the yawacceleration. That is, the component of the actuation signal forproducing the pressure peaks is determined as a function of the yawacceleration. Since the yaw moment which originates from the rollingmovement is proportional to the yaw acceleration, information is thusavailable as to which front wheel is to be braked in order to be able toproduce an anti-phase yaw moment for the rolling movement. The variableGier_Beschl_TP is acquired in the block 702 by lowpass filtering fromthe signal Gier_Beschl which is fed to said block.

If the flag Stab_Erk_P has the value 1 (a rolling movement of thevehicle combination 104 is occurring), the component of the actuationsignal which is made available by a block 807 and which brings about thepressure peaks is output. Otherwise the value 0 is output.

The product of the two variables Gier_Beschl_TP and Ein_Dyn_VL isdetermined using a multiplier 808, thereby converting the variableGier_Beschl_TP (which corresponds physically to a yaw acceleration) intoa variable P_Brems_VL which corresponds physically to a pressure. Thevariable P_Brems_VL is fed to the block 807.

In block 807, a signal is determined on the basis of the signalP_Brems_VL, and is output. This signal is used to carry out, at theleft-hand front wheel, such braking interventions which produce, ofcourse, in conjunction with corresponding braking interventions carriedout at the right-hand front wheel, a yaw moment which counteracts therolling movement.

As already explained, the signal Gier_Beschl_TP corresponds to the yawacceleration. In the mathematical sense, this signal constitutes thetime derivative of the profile 1 of the yaw angle rate which isillustrated in FIG. 2. (For the sake of clarity the signal profile ofthe yaw acceleration has not been illustrated in FIG. 2; however, it isessentially a signal which is offset by 90° and is an advance of thesignal of the yaw angle rate.) Both the signal Gier_Beschl_TP and thesignal P_Brems_VL exhibit an oscillating behavior.

In order to be able to generate on the basis of the oscillating signalP_Brems_VL a signal which can be used to carry out correctly phasedbraking interventions at the left-hand front wheel, the block 807 isembodied as a comparator which operates as follows:

Within the scope of the present exemplary embodiment the block 807 isintended only to output the positive signal components of the signalP_Brems_VL. For this purpose, the signal P_Brems_VL is compared with acomparative variable Eim_Dyn_Richt_VL in the block 8/7. If the signalP_Brems_VL equals or exceeds the value of the comparative variableEin_Dyn_Richt_VL, the amount of the excess of the signal P_Brems_VL isoutput by the block 807. The components of the signal P_Brems_VL whichundershoot the value of the comparative variable Ein_Dyn_Richt_VL arenot output; instead the block 807 outputs the signal 0.

The comparative variable Ein_Dyn_Richt_VL preferably has the value 0.Due to the definition of this value, the positive halfwaves of thesignal P_Brems_VL are output by block 807 and the negative halfwaves aresuppressed. The method of functioning of the block 807 can also bedescribed in such a way that it outputs the maximum value of the twovariables P_Brems_VL and Ein_Dyn_Richt_VL.

The block 802 which is used for the right-hand front wheel 103 vr in theblock 701 corresponds in terms of structure to that which is illustratedin FIG. 8 c, but with the difference that the factor Ein_Dyn_VR which isused for the right-hand front wheel 103 vr is negative. As a result, thenegative halfwaves which are contained in the signal Gier_Beschl_TP, fordetermining the actuation signal with which the pressure peaks areproduced at the right-hand front wheel 103 vr, are taken into accountfor the right-hand front wheel 103 vr, and the positive half waves arefiltered out.

To summarize it is to be noted that: the positive halfwaves of thesignal Gier_Beschl_TP are taken into account for the left-hand frontwheel 103 vl, and the negative halfwaves of said signal are taken intoaccount for the right-hand front wheel 103 vr.

After the method of operation of the two blocks 701 and 702 has beendescribed, the two blocks 703 and 704 which are illustrated in FIG. 7 bwill then be described.

Block 703 constitutes an ESP system which is arranged in the towingvehicle and with which the yaw angle rate of the towing vehicle iscontrolled. This ESP system has sensors for sensing the wheel speeds ofthe individual wheels of the towing vehicle, the steering angle, thelateral acceleration and the yaw angle rate. Using a vehicle speed whichis determined as a function of the wheel speeds, and the steering angle,a setpoint value for the yaw angle rate is determined by means of amathematical model. The setpoint value is compared with the actual valuewhich is determined for the yaw angle rate, and when a deviation ispresent, stabilizing wheel-specific braking interventions and engineinterventions are carried out. The braking interventions are used toproduce yaw moments which act on the towing vehicle and have the purposeof compensating an oversteering or understeering travel behavior of thetowing vehicle. The engine torque which is output by the engine isreduced using the engine interventions, which ultimately leads to areduction in the vehicle speed.

Signals S_ESP coming from the ESP system 703 are fed to the block 704.The signals S_ESP contain, inter alia, the actuation signals which aredetermined by the ESP system and have the purpose of carrying out thestabilizing braking interventions, and further signals which arerequired in the block 704, inter alia for determining the operatingstates of the vehicle combination. In this particular case these are thefollowing signals: i) a variable which describes the longitudinalacceleration of the vehicle combination; ii) a variable which describesthe coefficient of friction of the underlying surface on which thevehicle combination is moving (estimated, for example, on the basis of avariable which describes the lateral acceleration and a variable whichdescribes the longitudinal acceleration); and iii) a variable whichrepresents the braking requirement of the driver, and which representsthe activation of the brake pedal and/or the initial pressure set by thedriver. In addition, the flag Stab_Erk_P and the actuation signalsEHB_Eingriff_V which are produced using the two blocks 701 and 702 arefed to the block 704.

As long as the flag Stab_Erk_P has the value 0, (no rolling movement isoccurring for the vehicle combination), the actuation signals which areproduced by the ESP system 703 are output as signals EHB_Eingriff. Assoon as the flag Stab_Erk_P has the value 1 (a rolling movement isoccurring for the vehicle combination), the signals EHB_Eingriff_V whichare produced in the blocks 701 and 702 for the front wheels and theactuation signals for the rear wheels are output as signalsEHB_Eingriff, said actuation signals carrying out the brakinginterventions at the rear wheels which correspond to the respectiveoperating state. The actuation signals for the rear wheels are producedor modified in the block 704.

At this point it is to be noted that the function of the subordinateanti-lock brake system which is contained in the ESP system runs alongpermanently in the background. As soon as the tendency to lock isdetected for a wheel, appropriate braking interventions are performed inorder to reduce the brake pressure.

FIG. 9 is a block circuit diagram which shows both a schematicillustration of the device according to the invention and the essentialsteps of the method according to the invention which runs in the deviceaccording to the invention. At this point, no more details will be givenon the function or the structure of the blocks 301, 302, 401 and 402, asthe latter have already been described in detail above.

The following variables are fed to the detection logic component 301: i)the variable Delta_Gier_PID coming from the block 401; and ii) thevariable LW_Diff coming from the block 402. In addition, the variable V(vehicle speed) is fed to the detection logic component 301 coming froma block 901. The block 901 comprises wheel speed sensors which areassigned to the individual wheels of the towing vehicle 101 as well assuitable means with which the signals which are made available by thewheel speed sensors are converted into the variable V. As a function ofthese variables, the detection logic component 301 detects whether ornot a rolling movement is occurring for the vehicle combination 104. Ifso, the detection logic component 301 outputs the value 1 for the flagStab_Erk_P. When the value 1 is present for the flag Stab_Erk_P thevariables MOT_Eingriff and EHB_Eingriff are determined in theintervention logic component 302, and fed to a block 902. Stabilizingbraking interventions are carried out using the individual actuationsignals which are combined to form the variable EHB-Eingriff. For thispurpose, either brake actuators which are assigned directly to theindividual wheels of the towing vehicle 101 can be actuated by theseactuation signals or else these actuation signals are fed to a controldevice which is assigned to the brake system of the towing vehicle 101.In addition, engine interventions are preformed using the variableMot_Engriff. The block 902 comprises the brake actuators and/or thecontrol device which is assigned to the brake system of the towingvehicle and/or actuators for carrying out the engine interventions.

The vehicle can be equipped with a hydraulic, electrohydraulic,pneumatic, or electropneumatic, or electromechanical brake system. Theimportant factor is that the brake system can be used to carry outwheel-specific braking interventions which are independent of thedriver, specifically in such a way that a braking force can be built up,maintained or reduced at the individual wheels. This condition isfulfilled, for example, by brake systems such as are used nowadays invehicles that are equipped with a dynamic movement system (ESP). Such adynamic movement system is used to stabilize the vehicle about itsvertical axis by controlling the yaw angle rate.

In addition to, or instead of, the stabilizing braking interventions itis also possible, if the vehicle has a corresponding actuation system,to carry out stabilizing steering interventions. These steeringinterventions must also be carried out in a correctly phased way inaccordance with the stabilizing braking interventions so that thesteering interventions produce a yaw moment which counteracts therolling movement of the vehicle combination.

The vehicle combinations which are considered in conjunction with themethod and apparatus according to the invention are intended to be, forexample, combinations from the passenger car field which are composed ofa towing vehicle and a trailer, for example a motor home trailer, a cartransportation trailer or a boat trailer. However, it is alsoconceivable to use the method according to the invention and the deviceaccording to the invention in vehicle combination from the field ofutility vehicles, which are composed of a towing vehicle and asemitrailer or pole trailer.

Although the method according to the invention and the device accordingto the invention have been described above exclusively in conjunctionwith vehicle combinations, since the problem of rolling occurs to agreater degree with vehicle combinations and is far more dangerous withsuch combinations than in individual vehicles, it is to be noted at thispoint that the use of the device according to the invention and themethod according to the invention is also conceivable for individualvehicles.

To conclude, the idea on which the method according to the invention andthe device according to the invention are based will be summarized oncemore without taking into account the already existing prior art: Themethod according to the invention relates to a method for stabilizing avehicle combination which is composed of a towing vehicle and a trailer,wherein at least one dynamic movement input variable is determined andevaluated, and wherein a braking intervention and/or engine interventionfor stabilizing the dynamic movement state of the vehicle combinationfor is brought about for the towing vehicle if an unstable dynamicmovement state is detected by means of the evaluation.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1.-29. (canceled)
 30. A method for stabilizing a vehicle combination ofa trailer or semi-trailer and a towing vehicle having front wheels, saidmethod comprising: determining and evaluating at least one dynamicmovement input variable; if a rolling movement of the vehiclecombination is detected by means of the evaluation, implementing atleast braking interventions for stabilizing the dynamic movement stateof the vehicle combination for the towing vehicle; and producing a yawmoment which counteracts the rolling movement of the vehiclecombination, by means of braking interventions which are applied to thefront wheels of the towing vehicle; wherein, braking interventions areimplemented at the rear wheels of the towing vehicle; only when apredefined operating state of the vehicle combination is present; andthe braking interventions which are implemented at the rear wheelseffect an essentially constant braking at the rear wheels..
 31. Themethod as claimed in claim 30, wherein the predefined operating state ofthe vehicle combination, in which braking interventions are implementedat the rear wheels, is present if a rolling movement of the vehiclecombination is detected at a time when there is no braking by the driverand the vehicle combination is located on an underlying surface with alow coefficient of friction.
 32. The method as claimed in claim 30,wherein the predefined operating state of the vehicle combination inwhich braking interventions are implemented at the rear wheels ispresent if a rolling movement of the vehicle combination is detected andat a time when there is no braking by the driver and the brakinginterventions which are applied to the front wheels causes a risk of thefront wheels locking.
 33. The method as claimed in claim 30, whereinbraking interventions are implemented at the rear wheels if a rollingmovement of the vehicle combination is detected, there is no braking bythe driver, and the vehicle combination is located on an underlyingsurface with a low coefficient of friction.
 34. The method as claimed inclaim 30, wherein braking interventions are implemented at the rearwheels if a rolling movement of the vehicle combination is detected,there is no braking by the driver and the braking interventions whichare applied to the front wheels lead to a risk of the front wheelslocking.
 35. The method as claimed in claim 30, wherein the predefinedoperating state of the vehicle combination in which brakinginterventions is implemented at the rear wheels is present if a rollingmovement is detected during a driver initiated braking process, andvehicle deceleration occurring as a result of the driver initiatedbraking process fulfills a predefined comparative criterion.
 36. Themethod as claimed in claim 30, wherein braking interventions areimplemented at the rear wheels if a rolling movement is detected duringa driver initiated braking process, and vehicle deceleration occurringas a result of the driver initiated braking process fulfills apredefined comparative criterion.
 37. The method as claimed in claim 36,wherein if the vehicle deceleration which occurs is below a predefinedthreshold value, a braking effect at the rear wheels as a result of thedriver initiated braking process is at least partially reduced by thebraking interventions which are brought about for the rear wheels. 38.The method as claimed in claim 37, wherein the braking effect is reducedto such an extent that the value of the vehicle deceleration which hasoccurred as a result of the driver initiated braking process is at leastmaintained.
 39. The method as claimed in claim 36, wherein if thevehicle deceleration is above a predefined threshold value, the brakingeffect at the rear wheels as a result of the driver initiated brakingprocess is at least maintained by the braking interventions which areimplemented at the rear wheels.
 40. The method as claimed in claim 39,wherein if an intervention of an anti-lock brake system is made at orboth front wheels, an additional braking effect at the rear wheels isincreased by braking interventions which are implemented at the rearwheels.
 41. The method as claimed in claim 40, wherein the increase inthe additional braking effect at the rear axle is carried out in such away that the value of the vehicle deceleration which has occurred as aresult of the driver initiated braking process which is initiated ismaintained.
 42. The method as claimed in claim 30, wherein the brakinginterventions which are applied to the front wheels give rise to brakingforces which are composed of a basic force and a dynamic forcecomponent.
 43. The method as claimed in claim 30, wherein: at least thetowing vehicle is equipped with one of a hydraulic, an electrohydraulic,a pneumatic, and an electropneumatic brake system; and the brakinginterventions which are applied to the front wheels are such that abrake pressure which is composed of a basic pressure and dynamicpressure peaks is supplied to wheel brake cylinders assigned to thefront wheels.
 44. The method as claimed in claim 42, wherein a yawmoment which counteracts a rolling movement of the vehicle combinationis produced by the dynamic force component.
 45. The method as claimed inclaim 42, wherein a value of the basic force or pressure is determinedas a function of a deviation in a yaw angle rate, in particular thedeviation results from the difference between the actual value for theyaw angle rate which is determined using a yaw angle rate sensor and asetpoint value for the yaw angle rate which is determined using amathematical model.
 46. The method as claimed in claim 42, wherein thevalue for the dynamic force component is determined as a function of avariable which describes a change over time of a deviation in the yawangle rate.
 47. The method as claimed in claim 43, wherein both thebasic pressure and the dynamic pressure peaks decrease as the rollingmovement decreases.
 48. The method as claimed in claim 30, wherein:engine interventions are also carried out in addition to brakinginterventions; and a moment which is output by the engine is set bymeans of the engine interventions in such a way that substantially nocircumferential forces occur at the driven wheels of the towing vehicle.49. The method as claimed in claim 30, wherein: engine interventions arecarried out in addition to braking interventions; and torque which isoutput by the engine is set by the engine interventions in such a waythat friction losses which occur in the drive train are compensated andthe driven wheels are given a neutral setting as far as thecircumferential force is concerned.
 50. The method as claimed in claim30, wherein: after stabilizing braking interventions have beeninitiated, it is checked whether instability of the vehicle combinationdecreases; when the vehicle combination has returned to a stable state,no further stabilizing braking interventions are produced; and at thesame time drive torque is set in accordance with a value which ispredefined by the driver and which can be derived from the activation ofthe accelerator pedal.
 51. The method as claimed in claim 30, whereinbraking interventions are carried out at the front wheels as a functionof one of a value of sensed yaw moment which acts in the vehicle and avalue of the sensed yaw acceleration.
 52. The method as claimed in claim30, wherein at least a yaw angle rate of the towing vehicle isdetermined and evaluated as a dynamic movement input variable.
 53. Themethod as claimed in claim 30, wherein vehicle speed, yaw angle rate andsteering angle are evaluated to determine whether a rolling movement isoccurring.
 54. The method as claimed in claim 53, wherein a rollingmovement is occurring if the yaw angle rate exhibits an oscillatingbehavior in an operating state of the vehicle combination in which thevehicle speed is higher than an associated threshold value, even thoughthe driver is not making any steering interventions.
 55. The method asclaimed in claim 30, wherein the presence of a rolling movement of thevehicle combination is detected as a function of a deviation variablewhich includes a deviation between actual value of the yaw angle rateand an associated setpoint value.
 56. A device for stabilizing a vehiclecombination comprising a trailer and a towing vehicle that has frontwheels and rear wheels, said device comprising: means for determiningand evaluating at least one dynamic movement input variable; means forimplementing at least braking interventions at the front wheels of thetowing vehicle, for stabilizing the dynamic movement state of thevehicle combination if a rolling movement of the vehicle combination isdetected by means of the evaluation; wherein, a yaw moment whichcounteracts the rolling movement of the vehicle combination is producedby means of the braking interventions at the front wheels of the towingvehicle; braking interventions for the rear wheels of the towing vehicleare additionally permitted only when a predefined operating state of thevehicle combination is present; and the braking interventions which areadditionally permitted or brought about for the rear wheels effect anessentially constant braking effect at the rear wheels.